Embodiments of the invention relate generally to a Micro-Electro-Mechanical Systems (MEMS) switch and, more particularly, to a system and method for fault interruption using MEMS switches.
MEMS is a technology that in its most general form can be defined as miniaturized mechanical and electro-mechanical elements (i.e., devices and structures) that are made using the techniques of microfabrication. The critical physical dimensions of MEMS devices can vary from well below one micron on the lower end of the dimensional spectrum, all the way to several millimeters. Likewise, the types of MEMS devices can vary from relatively simple structures having no moving elements, to extremely complex electromechanical systems with multiple moving elements under the control of integrated microelectronics, with free-standing MEMS structures or “beams” often acting as relays, for example.
With respect to MEMS devices having moving elements, such a moving element may be in the form of a free-standing and suspended MEMS structure that is configured as a cantilever with a first end anchored to a substrate (e.g., fused silica, glass, silicon substrates) and a second free end having a contact. When the MEMS device is activated, the free-standing MEMS structure moves its contact against a substrate contact on the device substrate and under the MEMS structure contact.
With specific regard to MEMS switches, it is further recognized that—in operation—the contacting of the free-standing structure with the substrate contact can cause the free-standing structure (i.e., a contact of the free-standing structure) to experience mechanical wear due to repeated physical impact with the substrate contact, heating of the free-standing structure contact by joule heating, and electrical discharges between the free-standing structure contact and the substrate contact. This wearing of the free-standing structure contact can eventually lead to reliability issues in the MEMS switches.
One common reliability issue in MEMS switches resulting from the wearing of the free-standing structure contact is that the contact becomes stuck closed. Other conditions that can contribute to the stuck closed contact failure mode are arcing due to a hot switching condition, stiction due to van der Waals forces, plastic deformation of the beam, or gate driver failures when the MEMS switches are in the on condition. Depending on the system in which a MEMS switch is installed, the stuck closed fault condition can cause additional failures upstream or downstream of a stuck MEMS switch and can be especially problematic in applications that include a large number of MEMS switches.
It is recognized that the stuck closed failure mode in MEMS switches is not the only failure mode that can occur in electrical systems. Other failure modes include, for example, short circuits, open circuits, voltage transients or power surges or spikes, power failure, power sags, brownouts or undervoltage conditions, overvoltage conditions, electrical line noise, frequency variations, switching transients, harmonic distortion, and cooling system failures. As with the stuck closed failure mode in MEMS switches, any of the above-listed failures will cause damage to a system if it is not detected and managed properly.
Therefore, it is desirable to provide a fast acting and cost effective solution to interrupt circuits containing MEMS switches in electrical systems that are experiencing a failure.